Chromium oxide, deposited directly onto silica, is an active ethylene polymerization catalyst, (see U.S. Pat. No. 2,825,721 and McDaniel, M. P., A Review of the Phillips Supported Chromium Catalyst and Its Commercial Use for Ethylene Polymerization. Adventures in Catalysis. Bruce, C. G.; Helmut, K., Eds. Academic Press: 2010; Vol. 53, 123-606) as is chromocene (Cp2Cr) deposited on silica (see Karapinka, G. L. BE723775, 1968). Despite these discoveries being decades old, there is still much research to be done on chromium olefin polymerization catalysts. Specifically, discrete chromium(III) organometallic catalysts have received a lot of attention lately; such catalysts are of interest because the plastics they make may be useful to industry.
Half sandwich chromocenes are disclosed in DE 19710615; WO 2012/040147; US 2013/225820; US 2010/267901; and CN 102070732. In particular, J. Organometallics 2000, 19, 388-402 (Dohring, A. et al.) discloses ethylene(cyclopentadienyl) (pyrrolidine)chromium dichloride.
Other references of interest include: US 2012/059134: Macromol. Rapid Comm. 2010, 31, 1359-1363 (d. Kurek, A. et al.); WO 2011/089017; WO 2006/052232; WO 2008/140175; and U.S. Ser. No. 62/012,047 filed Jun. 13, 2014.
There is still a need in the art for new and improved catalyst systems for the polymerization of olefins, in order to achieve specific polymer properties, such as impact resistance without negatively impacting the resulting polymer's processability properties.
It is therefore an object of the present invention to provide novel catalyst compounds, catalyst systems comprising such compounds, and processes for the polymerization of olefins using such compounds and systems.